Amulet of Spell Funneling

This amulet carries a programmed spell inside that is beyond the reach of most casters. By willingly funneling spell energy into this amulet, casting higher spells can be accomplished by a group as easily as a high mage can alone.

Spell compacting: Creatures within 120 ft. of the amulet can use a reaction to willingly dedicate spell energy towards the cost of the stored spell. The stored spell can be any spell that the user is aware of and has seen before. 

Arcane conversions: Some spells cost more than others. The conversions are as thus.